VESPA GTV 250 i.e. 2008 Service Station Manual page 123

Vespa GTV 250 i.e.
- If the clearance is greater than that indicated in
the table, replace the piston.
N.B.
MEASURE THE CLEARANCE BY INSERTING THE BLADE
OF THE FEELER THICKNESS GAUGE FROM THE SECOND
SEAL SIDE.
N.B.
THE PIN HOUSINGS HAVE 2 LUBRICATION CHANNELS.
FOR THIS REASON MEASUREMENT OF THE DIAMETER
MUST BE CARRIED OUT ACCORDING TO THE AXIS OF
THE PISTON.
Characteristic
Wrist pin seat on the piston: Standard diameter
15.001 - 15.006 mm
Diameter of the wrist pin seat on the piston:
Standard clearance
0.001 - 0.010 mm
piston diameter
71.953 - 71.981 mm
Fitting clearance
1st compression ring - standard coupling
clearance
0.015 - 0.06 mm
maximum clearance allowed after use
2nd compression ring - standard coupling
clearance
0.015 - 0.06 mm
maximum clearance allowed after use
oil scraper ring - standard coupling clearance
oil scraper ring - maximum clear-
0.015 - 0.06 mm
ance allowed after use
Inspecting the cylinder
- Using a bore meter, measure the inner cylinder
diameter at three different points according to the
directions shown in the figure.
- Check that the head coupling surface is not worn
or misshapen.
- Pistons and cylinders are classified according to
their diameter. The coupling must be made with
those of the same type (M-M, N-N, O-O, P-P).
Characteristic
cylinder: standard diameter
71.990 - 72.018 mm (at 33 mm)
Maximum allowable run-out:
0.001 in 0.05 mm
1st compression ring -
0.07 mm
2nd compression ring -
0.07 mm
0.07 mm
Engine
ENG - 123